Implants are substances or parts that are introduced into the human or animal body to fulfill certain substitute functions for a limited period of time or for life. In contrast with transplants, implants are made of an artificial material (alloplasty). A distinction is often made between medicinal, plastic and functional implants.
Medicinal implants have the task of supporting or replacing body functions. Depending on function, the medicinal implants are also referred to as implantable prostheses. Examples of medicinal implants include, for example, heart pacemakers, brain pacemakers for Parkinson's disease, heart implants, cochlear implants, implants in dental medicine, stents and implants that serve to form a depot of a pharmaceutical substance and various forms of joint replacements.
Plastic implants are used in plastic surgery, e.g., to replace body parts that have been destroyed or to change existing body parts.
Functional implants are used to monitor human or animal functions by implanting radiofrequency identification (RFID) chips subcutaneously.
From the variety of existing types of implants, it is possible to discern that implants and their use in medicine have gained great importance.
Some considerable adverse effects are to be expected with traditional treatment principles, e.g., in systemic administration of one or more active ingredients, for example, in tumor therapy, so that local controlled release of active ingredients at the target site or in the vicinity thereof has been gaining increasing relevance (local drug delivery concept (LDD) concept). To be able to perform this local administration of active ingredients, implant base bodies, in particular, are coated with active ingredients which are implanted either at the target site or in its vicinity in a human or animal body and thereby release active ingredients. This method, which has been established clinically, is used millions of times worldwide each year and it is anticipated that demand for new materials and new forms of administration will grow in view of the demographic shift within the age pyramid.
In the orthopedic field, implant-associated infections and thromboembolic complications are known to occur in conjunction with endoprosthetic implants. Research has, therefore, been conducted with implants coated with active ingredients in this field, in particular, antibiotic-coated implants.
In the field of cardiovascular diseases, minimally invasive forms of treatment offer an increasingly well-established method of treatment for dilatation and stabilization of stenosed coronary vessels through percutaneous transluminal coronary angioplasty (PCTA) and stent implantation. To achieve a further reduction in the incidence of late complications, in particular, in repeat narrowing of a vessel after PCTA (in-stent restenosis (ISR)), especially in high-risk patients, current research has pursued the goal of local administration of the active ingredients by means of a medication-coated stent (drug eluting stents (DES)).
The incidence of complications occurring with the conventional methods of the LDD concept so far, which is not to be underestimated, is due to partial bolus-like release of the active ingredients at the site of administration which can result in a local overdose of the active ingredients.
Known drug eluting stents usually comprise an active ingredient which is present in dispersed form in a polymer coating and/or within a layer of a polymer coating such that the polymer coating containing the active ingredient is applied to the base body of the stent.
Such a polymer layer with the active ingredient incorporated into it usually has a layer thickness of 10 μm to 20 μm so that when the stent braces are coated on all sides the wall thickness of the stent is approximately doubled. Various investigations, in particular, the ISAR-STEREO study, have now found that the risk of restenosis after PCTA also increases with the increase in wall thickness of the stent.
Furthermore, with such a polymer coating, it may be difficult to achieve adequate pharmacokinetics of the active ingredients at the target site in the human or animal body.
International Patent Publication No. WO 2006/118937 discloses stents which are designed so that the release of active ingredients embedded in polymer matrices is controlled.
U.S. Pat. No. 6,753,071 discloses implantable medical products, in particular, stents, which have a coating that reduces the rate of release of the active ingredient incorporated into a polymer layer.